John Warnock’s ‘Camelot’ signalled birth of PDF

Editor’s Note: The ‘Camelot’ Paper: In the Spring of 1991, Dr. John Warnock first described the market opportunity for Acrobat in this document. Download a PDF version of Dr. Warnock’s original Camelot Project [PDF: 15kb] paper. Published on Planet PDF with the expressed permission of the author.

By Dr. John Warnock, Adobe Systems CEO, Spring of 1991

Camelot Paper
This document describes the base technology and ideas behind the
project named ‘Camelot.’ This project’s goal is to solve a fundamental
problem that confronts today’s companies. The problem is concerned
with our ability to communicate visual material between different
computer applications and systems. The specific problem is that most
programs print to a wide range of printers, but there is no universal
way to communicate and view this printed information
electronically. The popularity of FAX machines has given us a way to
send images around to produce remote paper, but the lack of quality,
the high communication bandwidth and the device specific nature of
FAX has made the solution less than desirable. What industries badly
need is a universal way to communicate documents across a wide
variety of machine configurations, operating systems and
communication networks. These documents should be viewable on
any display and should be printable on any modern printers. If this
problem can be solved, then the fundamental way people work will

The invention of the PostScript language has gone a long way to
solving this problem. PostScript is a device independent page
description language. Adobe’s PostScript interpreter has been
implemented on over 100 commercially available printer products.
These printer products include color machines, high resolution
machines, high speed machines and low-cost machines. Over 4000
applications output their printed material to PostScript machines.
This support for PostScript as a standard make the PostScript
solution a candidate for this electronic document interchange.
Within the PostScript and Display PostScript context the ‘view and
print anywhere’ problem has been implemented and solved. Since
most applications have PostScript print drivers, documents from a
wide variety of applications can be viewed from operating systems
that use Display PostScript. PostScript files can be shipped around
communication networks and printed remotely. ‘Encapsulated
PostScript’ is a type of PostScript file that can be used by many
applications to include a PostScript image as part of a page the
application builds.

The reason the Display PostScript and PostScript solutions are not a
total solution in today’s world is that this solution requires powerful
desktop machines and PostScript printers. The Display PostScript and
PostScript solutions are the correct long-term solution as the power
of machines increases over time, but this solution offers little help
for the vast majority of today’s users with today’s machines.
The Camelot Project is an attempt to define technologies and
products that will give the value that Display PostScript and
PostScript delivers to the vast number of installed machines that
exists today. For the purposes of this discussion these machines
include 640K Intel 286/386/486 machines (PC compatibles), Apple
Macintosh machines, mainframes, and workstations. The displays
must include CGA, EGA, VGA and any other higher resolution or color
displays supported by the above machines.

Our vision for Camelot is to provide a collection of utilities,
applications, and system software so that a corporation can
effectively capture documents from any application, send electronic
versions of these documents anywhere, and view and print these
documents on any machines.

There are at least two technical approaches to the Camelot project.
Both solutions depend on the PostScript technology. One approach is
to try to make Display PostScript and PostScript implementations
smaller and faster so that they can run on the vast majority of
today’s machines. This approach has been tried and is extremely

A second approach is to divide the problem into smaller problems.
This approach would allow each piece to run independently on the
smaller machines while achieving acceptable performance and a
solution for the complete problem. This latter approach requires that
the problem be divided in a way that is natural for users, and
provides a solution for every user. An approach to the Camelot
project will now be described that will divide the problem into
smaller pieces. This solution depends on a unique property of the
PostScript language.

PostScript, as an interpretive language, has some properties that
other interpretive languages do not have. In particular, the semantics
of operators is not fixed. Operators can be redefined to have any
desired behavior. This property of PostScript allows the execution of
a PostScript file to have side effects that are very different from the
normal printing of a page. An example might be instructive. Suppose
a PostScript file draws 10 sided polygon with the following PostScript

{1 0 moveto
/ang 36 def
10 {ang cos ang sin lineto
/ang ang 36 add def

This procedure will build a path that is a ten sided polygon. In this
procedure the verbs: ‘moveto’ and ‘lineto’ have the standard
semantics of building a PostScript path within the PostScript

By redefining ‘moveto’ and ‘lineto’ very different things can
happen. For example, if these operators are defined as follows:

{exch writenumber writenumber (moveto) writestring}def
{exch writenumber writenumber (lineto) writestring}def
then when the 'poly' procedure is executed a file is written that has
the following contents:
1.0 0.0 moveto
0.809 0.588 lineto
0.309 0.951 lineto
-0.309 0.951 lineto
-0.809 0.588 lineto
-1.0 0.0 lineto
-0.809 -0.588 lineto
-0.309 -0.951 lineto
0.309 -0.951 lineto
0.809 -0.588 lineto
1.0 0.0 lineto

In this example the new redefined ‘moveto’ and ‘lineto’ definitions
don’t build a path. Instead they write out the coordinates they have
been given and then write out the names of their own operations.
The resulting file that is written by these new definitions draws the
same polygon as the original file but only uses the ‘moveto’ and
‘lineto’ operators. Here, the execution of the PostScript file has
allowed a derivative file to be generated. In some sense this
derivative file is simpler and uses fewer operators than the original
PostScript file but has the same net effect. We will call this operation
of processing one PostScript file into another form of PostScript file

The above example illustrates a capability of the PostScript language
that is not frequently used. This ‘rebinding’ of the language,
however, is extremely valuable. The Camelot project depends on
variations on this idea.

The approach we will take with Camelot is to define a new language
of operators and conventions. For the purposes of this discussion we
will call this language ‘Interchange PostScript’ or IPS. IPS will
primarily contain the graphics and imaging operators of PostScript.

The language will be defined so that any IPS file is a valid PostScript
file. The file will have the appropriate baggage so that it is a valid
EPS file. IPS files will print on PostScript printer and will be able to
be used by applications that accept EPS files. IPS will also be
structured so that the complete PostScript parser is not necessary to
read any file written in IPS. IPS will have an adequate set of
operators so that any practical document expressed in PostScript can
be represented in IPS. There will be situations in IPS where the IPS
file cannot represent visual situations that can be theoretically
generated in PostScript. However we believe these situations are
extremely rare, and all practical application documents can be
represented efficiently in IPS. The right way to think about IPS is as
it relates to English. No person in the world knows every English
word, but a small subset of the English words, and certain usage
patterns enable people to consistently communicate.

Once we have defined IPS, we will build a version of the PostScript
interpreter (IPS binder) that will read any PostScript file and rebind
that file into an IPS file. The IPS binder can be quite small in that it
does not need the graphics, font or device machinery contained in
full PostScript interpreter. Another function of the IPS binder will be
to include reconstituted fonts into the IPS file. The idea here is to
include just the characters of a font that are actually used in the
document. A result of including the necessary characters from the
fonts used is that an IPS file will be completely self contained. In
other words, when I send a file around the country, I don’t have to
worry about whether the receiving location has all the fonts required
by the document. The current situation is that complex font
substitution schemes are used to deal with locations not having the
appropriate fonts.

Once IPS is defined and the IPS binder implemented, then users can
capture any PostScript file emitted by a PostScript driver, and
convert that file to a self contained IPS file. This file can be shipped
anywhere around the network and printed on any PostScript
machine (management utilities will be written to ease this printing

In addition to the IPS binder, a viewer and browser will be written
that will read IPS files, and render those files on displays or to dumb
raster printers. It is believed that IPS interpreters can be
substantially simpler, and smaller than full PostScript interpreters. It
is also believed that an IPS interpreter can have acceptable
performance on small machines. The real hope is to make the IPS
viewer and browser small enough so that it can co-exist with other
applications. It is interesting to think about what those applications
can be.

One obvious application for the IPS viewer is in its use in electronic
mail systems. Imagine being able to send full text and graphics
documents (newspapers, magazine articles, technical manuals etc.)
over electronic mail distribution networks. These documents could be
viewed on any machine and any selected document could be printed
locally. This capability would truly change the way information is
managed. Large centrally maintained databases of documents could
be accessed remotely and selectively printed remotely. This would
save millions of dollars in document inventory costs.

Specific large visual data bases like the value-line stock charts,
encyclopedias, atlases, Military maps, Service Manuals, Time-Life
Books etc. could be shipped on CD-ROM’s with a viewer. This would
allow full publication (text, graphics, images and all) to be viewed
and printed across a very large base of machines.

Imagine if the IPS viewer is also equipped with text searching
capabilities. In this case the user could find all documents that
contain a certain word or phrase, and then view that word or phrase
in context within the document.

Entire libraries could be archived in electronic form, and since IPS
files are self-contained, would be printable at any location.
One of the central requirements of the Camelot Project is that the IPS
file format is device independent. This is essential because it is
necessary to be able to print the documents on color or black and
white machines – on low or high resolution machines. This
requirement is also essential in order to visualize the documents at
various magnifications on the screen. For example, it is imperative
that the user be able to magnify portions of complex maps, so that
subportions of the image are easy to read even on low resolution

To accomplish the above requirement it is necessary that consistent
font rendering machinery be available to the viewer. For this reason
the viewers will need to contain the full ATM implementations as
part of each system.

In considering all the requirements of corporations regarding
documents, it is important to structure Camelot components so that
they can be sold in ways that are useful to the corporations. Several
ideas have come to mind.

Components of Camelot are generally not interesting to single users.
The exception to this is in the distribution of large generally useful
databases. If someone produced a CD-ROM with ‘maps of the world’
on it, then one can imagine selling a retail package with one viewer
and the CD-ROM.

In most other applications, the distribution of information is to many
people. In these latter cases a corporation would like a copy of the
viewer for every PC. One can imagine viewers integrated into mail
systems, or as general stand-alone browsing systems. In any event
corporations should be interested in site-licensing arrangements.
(more to come)

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